From the NHDES web site:
Throughout history, freshwater mussels have been used by humans as important components of tools and jewelry. Native Americans also used freshwater mussels as a supplemental food
source. Although most species are edible, freshwater mussels are not as tasty as their saltwater relatives. In addition, since they are long-lived filter feeders, pollutants can easily settle and buildup inside them, making them distasteful and potentially unhealthy for human consumption.
However, fresh-water mussels are eagerly consumed by other members of the food chain,
including raccoons, otters, and aquatic birds. Mussels also serve the aquatic ecosystem by
filtering debris out of water, making the aquatic environment more suitable for other freshwater
life.
This link should work for the full fact sheet:
http://des.nh.gov/organization/commi...ents/bb-55.pdf